<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8" />
    <title>Add a new layer below labels</title>
    <meta
      name="viewport"
      content="initial-scale=1,maximum-scale=1,user-scalable=no"
    />
    <script src="../../lib/mapbox-gl.js"></script>
    <link href="../../lib/mapbox-gl.css" rel="stylesheet" />
    <script src="../../lib/axios.min.js"></script>
    <style>
      body {
        margin: 0;
        padding: 0;
      }
      #map {
        position: absolute;
        top: 0;
        bottom: 0;
        width: 100%;
      }
    </style>
  </head>
  <body>
    <div id="map"></div>
    <script>
      let baseDataUrl = `http://${localStorage.getItem(
        "host"
      )}/mapbox-gl-js-offline-examples`;
      axios
        .get(
          baseDataUrl +
            `/resources/styles/${localStorage.getItem(
              "mbtilesStylesName"
            )}.json`
        )
        .then((res) => {
          let data = res.data;
          initMap(data);
        })
        .catch((err) => {
          console.error(err);
        });

      function initMap(style) {
        let map = new mapboxgl.Map({
          container: "map",
          center: [121.163, 31.161],
          zoom: 6.65,
          style: style,
        });

        map.on("load", function () {
          var layers = map.getStyle().layers;
          // Find the index of the first symbol layer in the map style
          var firstSymbolId;
          for (var i = 0; i < layers.length; i++) {
            if (layers[i].type === "symbol") {
              firstSymbolId = layers[i].id;
              break;
            }
          }
          map.addSource("urban-areas", {
            type: "geojson",
            data: baseDataUrl + "/data/geojson/ne_50m_urban_areas.geojson",
          });
          map.addLayer(
            {
              id: "urban-areas-fill",
              type: "fill",
              source: "urban-areas",
              layout: {},
              paint: {
                "fill-color": "#f08",
                "fill-opacity": 0.4,
              },
              // This is the important part of this example: the addLayer
              // method takes 2 arguments: the layer as an object, and a string
              // representing another layer's name. if the other layer
              // exists in the stylesheet already, the new layer will be positioned
              // right before that layer in the stack, making it possible to put
              // 'overlays' anywhere in the layer stack.
              // Insert the layer beneath the first symbol layer.
            },
            firstSymbolId
          );
        });
      }
    </script>
  </body>
</html>
